/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.scheduling.support;

import java.util.Date;
import java.util.concurrent.TimeUnit;

import org.springframework.lang.Nullable;
import org.springframework.scheduling.Trigger;
import org.springframework.scheduling.TriggerContext;
import org.springframework.util.Assert;

/**
 * A trigger for periodic task execution. The period may be applied as either
 * fixed-rate or fixed-delay, and an initial delay value may also be configured.
 * The default initial delay is 0, and the default behavior is fixed-delay
 * (i.e. the interval between successive executions is measured from each
 * <i>completion</i> time). To measure the interval between the
 * scheduled <i>start</i> time of each execution instead, set the
 * 'fixedRate' property to {@code true}.
 *
 * <p>Note that the TaskScheduler interface already defines methods for scheduling
 * tasks at fixed-rate or with fixed-delay. Both also support an optional value
 * for the initial delay. Those methods should be used directly whenever
 * possible. The value of this Trigger implementation is that it can be used
 * within components that rely on the Trigger abstraction. For example, it may
 * be convenient to allow periodic triggers, cron-based triggers, and even
 * custom Trigger implementations to be used interchangeably.
 *
 * @author Mark Fisher
 * @since 3.0
 */
public class PeriodicTrigger implements Trigger {

    private final long period;

    private final TimeUnit timeUnit;

    private volatile long initialDelay = 0;

    private volatile boolean fixedRate = false;


    /**
     * Create a trigger with the given period in milliseconds.
     */
    public PeriodicTrigger(long period) {
        this(period, null);
    }

    /**
     * Create a trigger with the given period and time unit. The time unit will
     * apply not only to the period but also to any 'initialDelay' value, if
     * configured on this Trigger later via {@link #setInitialDelay(long)}.
     */
    public PeriodicTrigger(long period, @Nullable TimeUnit timeUnit) {
        Assert.isTrue(period >= 0, "period must not be negative");
        this.timeUnit = (timeUnit != null ? timeUnit : TimeUnit.MILLISECONDS);
        this.period = this.timeUnit.toMillis(period);
    }


    /**
     * Return this trigger's period.
     *
     * @since 5.0.2
     */
    public long getPeriod() {
        return this.period;
    }

    /**
     * Return this trigger's time unit (milliseconds by default).
     *
     * @since 5.0.2
     */
    public TimeUnit getTimeUnit() {
        return this.timeUnit;
    }

    /**
     * Return the initial delay, or 0 if none.
     *
     * @since 5.0.2
     */
    public long getInitialDelay() {
        return this.initialDelay;
    }

    /**
     * Specify the delay for the initial execution. It will be evaluated in
     * terms of this trigger's {@link TimeUnit}. If no time unit was explicitly
     * provided upon instantiation, the default is milliseconds.
     */
    public void setInitialDelay(long initialDelay) {
        this.initialDelay = this.timeUnit.toMillis(initialDelay);
    }

    /**
     * Return whether this trigger uses fixed rate ({@code true}) or
     * fixed delay ({@code false}) behavior.
     *
     * @since 5.0.2
     */
    public boolean isFixedRate() {
        return this.fixedRate;
    }

    /**
     * Specify whether the periodic interval should be measured between the
     * scheduled start times rather than between actual completion times.
     * The latter, "fixed delay" behavior, is the default.
     */
    public void setFixedRate(boolean fixedRate) {
        this.fixedRate = fixedRate;
    }

    /**
     * Returns the time after which a task should run again.
     */
    @Override
    public Date nextExecutionTime(TriggerContext triggerContext) {
        Date lastExecution = triggerContext.lastScheduledExecutionTime();
        Date lastCompletion = triggerContext.lastCompletionTime();
        if (lastExecution == null || lastCompletion == null) {
            return new Date(System.currentTimeMillis() + this.initialDelay);
        }
        if (this.fixedRate) {
            return new Date(lastExecution.getTime() + this.period);
        }
        return new Date(lastCompletion.getTime() + this.period);
    }


    @Override
    public boolean equals(Object other) {
        if (this == other) {
            return true;
        }
        if (!(other instanceof PeriodicTrigger)) {
            return false;
        }
        PeriodicTrigger otherTrigger = (PeriodicTrigger) other;
        return (this.fixedRate == otherTrigger.fixedRate && this.initialDelay == otherTrigger.initialDelay &&
                this.period == otherTrigger.period);
    }

    @Override
    public int hashCode() {
        return (this.fixedRate ? 17 : 29) + (int) (37 * this.period) + (int) (41 * this.initialDelay);
    }

}
